The present invention concerns a device for assembling bags of foil material, and in particular a device for stacking bags of thin-walled material comprising a rotatable drum interacting with a supply and with a discharge conveyor, the periphery of said drum comprising assembling locations for stacked bags and retaining means (detents) for these stacked bags.
In order to promote the said stacking of bags there is located behind a fast operating bag machine or a bag cutting machine, a device to assemble said bags or, instead of bags sheets, in proper stacks. When a stack (bundle) comprising a predetermined number of bags or sheets is formed, the stack so formed is discharged. In practice these stacks of bags are generally received between discharge belts the velocity of transfer of which almost corresponds to the circumferential velocity of the drum of the machine.
By means of the supply conveyor the supplied bags are positioned upon a correct location at the circumference of a drum, pins being present upon which the open edge of the bags is pricked, in order to finally assemble a stack of separate bags upon the said pins.
A drum of this type provided with pins running according to a describing line (a generatrix) of the drum, can, however, only be employed when the supply of bags, comprising for example a sealed bottom, is so supplied that--as seen in the direction of travel--the bottom of the bags lies at the trailing end whereby the open side of the bag remains at the front, thus causing a row of small apertures along the open side of the bag to be unimpeding.
Should the bottom of the supplied bags be located in front or at the sides of the drum, then the result will be that an assembly of supplied bags being pricked upon a stacking drum, becomes inconvenient, since in these circumstances the apertures caused by the pins are detrimental for the bags.
Efforts have been made to provide a drum comprising two retaining devices, operating independently with respect to one another, and being positioned upon the circumference of the drum in front of each assembling location (stacking location). Said retaining devices had the shape of, for example, two curved fingers.
The solution as described hereinbefore caused a good and accurate supply and positioning of the bags upon the drum. Nevertheless the said solution offered various disadvantages, one of which was that the supply of a bag to a pack already assembled upon the circumference of the drum, caused the inner finger retaining the front edge of a packet of bags upon a location on the circumference of the drum, to lift the front edge of the bag still to be added. The result of this was that said edge was not put down fast enough upon the stack of bags, so that the operation of the machine was hampered.
The said disadvantage especially occurred in bags manufactured of slack, thin polyethylene foils, but could also be induced by a resistance of air at a high rotational velocity of the relative drum. The raised front edge of the bag lastly supplied impeded the formation of a pack, especially when the operational velocity of the drum was increased.
Owing to the latter feature further efforts have been made to retain the packets of bags upon the circumference of a drum by the use of belts or strings, partially enclosing the drum and having a velocity being adjusted as accurately as possible to the circumferential velocity of said drum.
In practice the fact has emerged that the velocity of the said belts or strings cannot possibly be adjusted appropriately to the circumferential velocity of the drum. Not only a so-called stripping of the lastly supplied bag will occur, but the inner layers of a pack of bags upon the drum may easily shift owing to the very smooth quality of the material from which they are manufactured.
This phenomenon especially occurs when the thickness of the pack of bags increases so that the relative diameter of the drum increases too, thus impeding the adaptability of the strings to the diameter of the drum and the thickness of the pack of bags.